Lab Report 1 Table of Contents 1 Profiles Layout 9 Points 2 Process Procedures 20 points 3 Calculations 36 Points 4 Questions 35 Points 5 Bonus Questions 10 Points Total Points 110 possible graded out of 100 Please be sure to include the requirement signature regarding academic honesty All lab group members should print out this page sign on the attached form and include it with your Lab Report Thank you REPORTS MUST BE WORD PROCESSED EXCEPT FOR SKETCHES AND HAND WRITTEN CALCULATIONS IF YOU MAKE AN ASSUMPTION PLEASE STATE IT CLEARLY PARTIAL CREDIT WILL BE GIVEN EVEN IF THE ANSWER IS NUMERICALLY WRONG Each group of two students will submit one joint report The report should be organized as follows 1 Profiles Layout 9 Points A Draw cross sectional profiles of a thin oxide MOSFET test structure 8 after each of the 11 major processing steps Indicate all layers and specify important details such as the non planar interfaces isotropic etch profiles point source Al evaporation thermal oxidation growth etc Label each feature and indicate thicknesses make roughly proportional sketches These drawings should have significantly more detail than those on the lab manual website See the diagram below for the exact cross sections in question 5 Points Pay attention to details such as consumption of Si during oxidation and isotropic etching profiles and directional metal deposition B Draw top views of the same thin oxide MOSFET test structure 8 after each of the four photolithography steps 4 Points 2 Process Procedures 20 Points A List and concisely describe the problems occurred during the fabrication in the class i e nonuniform film deposition etc Specifically these are the steps where all the wafers were run in batch i e oxidation poly deposition metallization What were the sources of the problems and how did you avoid them Was there any process step during your lab section that deviated from the descriptions in the lab manual If so why were some steps done differently and how did it affect the outcome How do you expect it to affect the performance function of the device 7 Points B Other than the problems that occurred during the session what were the particular problems or deviations from the rest of the groups that occurred in YOUR wafer Specifically these are the steps where all the wafers were run in individual processes i e photolithography etch etc What were the causes and how were the problems overcome Include any pictures sketches that would be helpful 7 Points C Describe monitoring measurements that were done during processing color line width thickness resistivity etc Determine and describe whether and how much each layer was overetched or underetched Did you purposely over underetch Why How much each layer was misaligned to the neighboring layers How much the misalignment acceptable in terms of the device function You may want to provide pictures taken to determine over underetch and misalignment 6 Points We are looking to see that you understand how the process steps work 3 Calculations 36 Points FOR CALCULATIONS USE PROCESS CONDITIONS ENCOUNTERED DURING YOUR LAB SESSION Calculate the parameters asked for in the following questions list both the theoretical values and the empirical values when applicable We would like to see that you understand what processing abnormalities may have led to a discrepancy between the two 1 Theoretical and empirical thicknesses of field oxide gate and intermediate oxides Include orientation dependence of oxidation rate but not impurity dependence 11 points 2 Junction depths after pre diffusion and drive in theoretical assume only phosphorous doping with surface concentration limited by solid solubility 12 points 3 Final surface concentrations of dopants as calculated using sheet resistance measurements made in lab Plot of sketch the change of dopant profile after each thermal step Label significant points such as peak concentration peak width junction depth and show non ideal effects such as dopant redistribution during oxidation Field Ox Gate Ox Poly Dep Pre Dep Drive In Sintering 6 points 4 Lateral diffusion under the MOSFET gates You may estimate but provide justification for estimation theoretical 4 points 5 Draw a table with the following parameters from your own wafer summarizing your calculation example table attached at end of document 3 points a Film Thickness all layers b Sheet Resistance ACTV after field oxidation after S D predeposition and drive in poly Si c Overetch Underetch all layers 4 Questions 35 Points Answer these questions in the most concise manner possible A few lines should suffice for each 1 What type of photoresist positive or negative I line or G line do we use in the lab Briefly describe how the resist responds to the process steps like spinning UV light exposure and development 2 points 2 What is the purpose of baking the wafers at 120 C before depositing HMDS What is the purpose of the 90 C bake after spinning on photoresist What happens if the soft bake is too hot say 150 C 2 points 3 What is the purpose of hard bake What happens if we skip this step What may happen if the bake is done at a temperature above 120 C say 150 C 2 points 4 We do lithography steps under yellow light only What happens if we expose the wafers to fluorescent light before development And after development Would red light damage your process 2 points 5 What are the differences between wet and dry oxidation that lead us to use one for the gate oxide and one for the field oxide What is the purpose of annealing in nitrogen after gate oxidation 2 points 6 How do you determine etching time using theoretical etch rate in literature List two ways to determine etch time empirically from lab measurements when you etch the layers Hint these methods include visual cues How close are the experimental and the theoretically calculated values 2 points 7 Before n deposition prior to SOG spinning we clean in Piranha but not in HF Before gate oxidation we clean in both Why the difference 2 points 8 Why is 5 1 BHF 5 1 NH4F HF used for etching features in the oxide while 10 1 BHF is used for cleaning and p glass stripping Why buffered HF 2 points 9 What would happen if we skipped the HF dip before metallization 2 points 10 What is selectivity What is the selectivity of HF between Si oxide and PR 2 points 11 Why do we first use the roughing pump and then the turbomolecular pump when pumping down the aluminum deposition system Why must the foreline pressure be kept
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